A downhole carbon dioxide transcritical boosting device and its working method

Abstract

The present invention relates to a downhole carbon dioxide transcritical boosting device and a working method thereof, which belong to the field of unconventional oil and gas resource development. The device comprises a carbon dioxide tanker, a mud pump, a cyclone desander, a double-wall drill pipe, a casing, a screw motor, a screw joint, a power shaft, a first-stage boosting unit, a first-stage boosting piston, a second-stage boosting unit, a second-stage boosting piston, a mixing chamber, a pump outlet chamber, a relief valve, a packer pin shaft, a track groove and a working method thereof. The downhole boosting system is driven by circulating drilling fluid as a power medium, and the CO2 is gradually pressurized and then injected into the formation, thereby overcoming the conventional CO2 formation injection technology, which requires high CO2 corrosion resistance for surface boosting equipment, well pipelines, etc. By utilizing the downhole boosting technology proposed by the present invention, conventional equipment in the oil field can be used for surface devices and double-wall drill pipes in the well, and only the downhole boosting system is required to have CO2 corrosion resistance, which can greatly save economic costs.

Description

Technical Field

[0001] The present invention belongs to the field of unconventional oil and gas resource development, and in particular relates to a downhole carbon dioxide transcritical pressurization method. Background Art

[0002] A supercritical fluid is a fluid whose temperature and pressure are simultaneously above their critical values. Its density approaches that of a liquid, while its viscosity and diffusion coefficient are similar to those of a gas. Supercritical fluids not only possess dissolution and extraction capabilities comparable to liquid solvents, but also possess heat and mass transfer rates far exceeding those of liquids. The critical temperature of CO2 is 31.5°C, and its critical pressure is 7.38 MPa. Supercritical CO2 formation injection technology is widely used in the following fields:

[0003] (1) Supercritical CO2 fracturing. Supercritical CO2 fracturing technology is particularly suitable for the transformation of unconventional oil and gas reservoirs with water sensitivity, water lock effect, low yield, and low permeability. The low viscosity and high diffusivity of supercritical CO2 increase the pore pressure and reduce the reservoir fracturing pressure. Supercritical CO2 can enter the micro-fracture pores, destroy the rock mineral cementation, cause the rock minerals to fall off and form self-support, and enhance the formation conductivity.

[0004] (2) Supercritical CO2 extraction of crude oil. CO2 has good fluidity in the supercritical state and has a strong ability to extract crude oil. After supercritical CO2 is injected into a tight oil reservoir, CO2 and crude oil become miscible, which can significantly improve the oil reservoir recovery rate.

[0005] (3) Shale oil CO2 huff-and-puff production increase. Injecting supercritical CO2 can improve crude oil properties, reduce oil-gas interfacial tension, and improve mobility ratio, making it an effective measure to increase shale reservoir recovery. Using a soaking process during the huff-and-puff process can ensure more complete oil-gas contact, help improve crude oil properties, and increase shale oil recovery.

[0006] (4) Carbon storage in formations. Supercritical CO2 has the advantages of high compressibility, high density and low viscosity. It can be stored at high density in formations such as saline water layers, seabeds, and coal seam goafs.

[0007] Supercritical CO2 has shown many advantages in increasing fracture complexity, replenishing formation energy, and improving crude oil fluidity. As an emerging fracturing technology, supercritical CO2 fracturing has incomplete related technologies. Supercritical CO2 injection technology has the following engineering challenges: (1) Supercritical CO2 formation injection requires complex surface equipment; (2) Supercritical CO2 is highly corrosive and requires dedicated surface equipment and well drilling tools, significantly increasing construction costs; (3) Affected by formation temperature and pressure, the phase state of CO2 in the well is uncertain, making construction difficult.

[0008] Therefore, there is an urgent need for a technology to solve the above problems in the prior art. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a device and a system for solving the problems existing in the background technology.

[0010] A downhole carbon dioxide transcritical pressurization device, characterized by comprising a double-wall drill pipe, a packer and a downhole pressurization system;

[0011] The double-wall drill pipe, packer and downhole pressurization system are all arranged downhole, and the number of the packers is three or more;

[0012] The double-wall drill pipe is provided with a casing, and the portion outside the casing well is connected to the inlet of a cyclone desander, the outlet of the cyclone desander is connected to the inlet of a mud pump, and the outlet of the mud pump is connected to the central channel of the double-wall drill pipe; the annular gap of the double-wall drill pipe is connected to a carbon dioxide tanker;

[0013] The downhole boosting system includes a screw motor, a screw joint, a power shaft, a first-stage boosting unit, a first-stage boosting piston, a second-stage boosting unit, a second-stage boosting piston, a mixing chamber and a pump-out chamber;

[0014] The screw motor is connected to the power shaft through a screw joint, and the connection between the screw joint and the power shaft is a sleeve connection. A pin is provided on the screw joint, and a track groove corresponding to the pin is provided on the power shaft;

[0015] The power shaft is connected to the first-stage booster piston and the second-stage booster piston in sequence.

[0016] The first-stage boosting unit and the second-stage boosting unit are piston cylinders, each of which is provided with a first-stage boosting piston and a second-stage boosting piston;

[0017] The secondary booster piston passes through the packer and is connected to the mixing chamber, and the mixing chamber passes through the packer and is connected to the pump-out chamber;

[0018] A proppant is arranged in the mixing chamber.

[0019] The ends of the first-stage boosting unit and the second-stage boosting unit are both provided with overflow valves.

[0020] A central channel is provided in the screw motor, and one end of the central channel is connected to the annular gap of the double-wall drill pipe.

[0021] The screw joint performs rotational motion, and the pin shaft cooperates with the track groove, so that the power shaft performs reciprocating motion in a straight line.

[0022] A method for downhole carbon dioxide transcritical pressurization, using any of the downhole carbon dioxide transcritical pressurization equipment described above, is characterized by comprising the following steps, which are performed in sequence:

[0023] Step 1

[0024] After the vertical well and the horizontal well are drilled, a packer and a downhole pressurization system are lowered; the mixing chamber of the downhole pressurization system is pre-filled with a proppant;

[0025] Step 2

[0026] Install the double-wall drill pipe and connect it to the downhole boosting system; connect the CO2 tanker to the annular gap of the double-wall drill pipe, and the CO2 enters the first and second boosting units through the central channel of the screw motor;

[0027] Step 3

[0028] The mud pump is connected to the central channel of the double-wall drill pipe and delivers drilling fluid into the central channel. Under the pressure of the drilling fluid, the screw motor rotates, driving the screw joint. The power shaft performs linear reciprocating motion under the cooperation of the pin shaft and the track groove, driving the first and second booster pistons to work.

[0029] Step 4

[0030] After the driving in step 3, the low-pressure gaseous carbon dioxide delivered by the carbon dioxide tanker is pressurized by the first-stage booster unit, and the carbon dioxide is pressurized to a supercritical state. The supercritical carbon dioxide is further pressurized in the second-stage booster unit to form a higher-pressure supercritical carbon dioxide.

[0031] Step 5

[0032] The supercritical carbon dioxide obtained in step 4 is mixed with the proppant in the mixing chamber to obtain a mixture; the mixture enters the pump-out chamber, the overflow valve opens under pressure, and the mixture of supercritical carbon dioxide and proppant passes through the overflow valve into the closed space isolated by the packer, and the mixture is injected into the bottom carbon storage space under pressure;

[0033] Step 6

[0034] The mixture injected into the bottom layer has a corrosive effect on the surrounding rock formations, causing rock blocks to peel off; the mud pump and carbon dioxide tanker stop working, and the downhole booster system performs a pressure relief operation. The peeled rock blocks and the mixture jointly support the cracks, forming a stable carbon storage space.

[0035] Before running into the downhole pressurization system in step 1, the density of the pre-filled proppant should be determined according to the density of supercritical carbon dioxide at the target pressure value. The density of the proppant can be adjusted by controlling the porosity of the proppant particles or the thickness of the resin coating.

[0036] Through the above-mentioned design scheme, the present invention can bring the following beneficial effects: the present invention utilizes circulating drilling fluid as a power medium to drive the downhole pressurization system, gradually pressurizes CO2, and then injects it into the formation, overcoming the conventional CO2 formation injection technology, which requires surface pressurization equipment, well pipelines, etc. to have high CO2 corrosion resistance. By utilizing the downhole pressurization technology proposed by the present invention, surface equipment and double-wall drill pipes in the well can adopt conventional equipment in the oil field, and only require the downhole pressurization system to have CO2 corrosion resistance, which can greatly save economic costs; in addition, the downhole pressurization technology proposed by the present invention can simplify surface equipment, and has advantages in construction in mountains, hills and other terrains. For submarine formation CO2 injection projects, it can reduce the demand for deck bearing capacity and realize efficient submarine carbon injection. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0038] Figure 1 It is a structural schematic diagram of the present invention;

[0039] Figure 2 This is an expanded view of the side surface of the power shaft in the present invention;

[0040] In the figure: 1-CO2 tanker, 2-mud pump, 3-cyclone desander, 4-double-wall drill pipe, 6-center channel, 7-casing, 8-screw motor, 9-screw joint, 10-power shaft, 11-first-stage booster unit, 12-first-stage booster piston, 13-second-stage booster unit, 14-second-stage booster piston, 15-mixing chamber, 16-pump outlet chamber, 17-relief valve, 18-packer, 19-crack, 21-pin shaft, 22-track groove. DETAILED DESCRIPTION

[0041] This application is further described with reference to the accompanying drawings:

[0042] A downhole carbon dioxide transcritical pressurization device, characterized by comprising a double-wall drill pipe 4, a packer and a downhole pressurization system;

[0043] The double-wall drill pipe 4, the packer and the downhole pressurization system are all arranged downhole, and the number of the packers is more than three;

[0044] A casing 7 is provided outside the double-wall drill pipe 4, and the portion of the casing 7 outside the well is connected to the inlet of the cyclone desander 3, the outlet of the cyclone desander 3 is connected to the inlet of the mud pump 2, and the outlet of the mud pump 2 is connected to the central channel 6 of the double-wall drill pipe 4; the annular gap of the double-wall drill pipe 4 is connected to the carbon dioxide tanker 1;

[0045] The downhole boosting system includes a screw motor 8, a screw joint 9, a power shaft 10, a primary boosting unit 11, a primary boosting piston 12, a secondary boosting unit 13, a secondary boosting piston 14, a mixing chamber 15 and a pumping chamber 16;

[0046] The screw motor 8 is connected to the power shaft 10 via a screw joint 9, and the connection between the screw joint 9 and the power shaft 10 is a sleeve connection. The screw joint 9 is provided with a pin 21, and the power shaft 10 is provided with a track groove 22 corresponding to the pin 21;

[0047] The power shaft 10 is connected to the first-stage booster piston 12 and the second-stage booster piston 14 in sequence.

[0048] The first-stage boosting unit 11 and the second-stage boosting unit 13 are piston cylinders, each of which is provided with a first-stage boosting piston 12 and a second-stage boosting piston 14;

[0049] The secondary booster piston 14 passes through the packer and is connected to the mixing chamber 15, and the mixing chamber 15 passes through the packer and is connected to the pump-out chamber 16;

[0050] The mixing chamber 15 is provided with a proppant.

[0051] The ends of the first-stage boosting unit 11 and the second-stage boosting unit 13 are both provided with overflow valves.

[0052] A central channel is provided in the screw motor 8 , and one end of the central channel is connected to the annular gap of the double-wall drill pipe 4 .

[0053] The screw joint 9 performs rotational motion, and the pin shaft 21 cooperates with the track groove 22, so that the power shaft 10 performs reciprocating motion in a straight line.

[0054] A method for downhole carbon dioxide transcritical pressurization, using any of the downhole carbon dioxide transcritical pressurization equipment described above, is characterized by comprising the following steps, which are performed in sequence:

[0055] Step 1

[0056] After the vertical well and the horizontal well are drilled, the packer and the downhole pressurization system are lowered; the mixing chamber 15 of the downhole pressurization system is pre-filled with proppant;

[0057] Step 2

[0058] Install the double-wall drill pipe 4 and connect it to the downhole boosting system; connect the CO2 tanker 1 to the annular gap of the double-wall drill pipe 4, and the CO2 enters the primary boosting unit 11 and the secondary boosting unit 13 through the central channel of the screw motor 8;

[0059] Step 3

[0060] The mud pump 2 is connected to the central channel 6 of the double-wall drill pipe 4 and delivers drilling fluid into the central channel 6. Under the pressure of the drilling fluid, the screw motor 8 rotates, driving the screw joint 9. The power shaft 10 performs linear reciprocating motion under the cooperation of the pin 21 and the track groove 22, driving the first-stage booster piston 12 and the second-stage booster piston 14 to operate.

[0061] Step 4

[0062] After the driving in step 3, the low-pressure gaseous carbon dioxide delivered by the carbon dioxide tanker 1 is pressurized by the first-stage booster unit 11, and the carbon dioxide is pressurized to a supercritical state. The supercritical carbon dioxide is further pressurized in the second-stage booster unit 13 to form supercritical carbon dioxide with a higher pressure.

[0063] Step 5

[0064] The supercritical carbon dioxide obtained in step 4 is mixed with the proppant in the mixing chamber 15 to obtain a mixture; the mixture enters the pumping chamber 16, and the relief valve 17 is opened under the action of pressure. The mixture of supercritical carbon dioxide and proppant passes through the relief valve 17 and enters the closed space isolated by the packer 18. Under the action of pressure, the mixture is injected into the bottom carbon storage space;

[0065] Step 6

[0066] The mixture injected into the bottom layer has a corrosive effect on the surrounding rock formations, causing rock blocks to peel off; the mud pump 2 and the carbon dioxide tanker 1 stop working, and the downhole booster system performs a pressure relief operation. The peeled rock blocks and the mixture jointly support the cracks 19, forming a stable carbon storage space.

[0067] Before running into the downhole pressurization system in step 1, the density of the pre-filled proppant should be determined according to the density of supercritical carbon dioxide at the target pressure value. The density of the proppant can be adjusted by controlling the porosity of the proppant particles or the thickness of the resin coating.

[0068] The principle of reciprocating motion of the power shaft 10: the screw joint 9 and the pin 21 rotate with the screw motor 8, and the pin 21 slides in the track groove 22 on the power shaft 10. The plane of the track groove 22 on the power shaft 10 is unfolded as shown in FIG. Figure 2 As shown, the mutual rotation motion of the pin shaft 21 is converted into a periodic reciprocating motion under the cooperation of the track groove 22.

[0069] The principle of progressive boosting: A reciprocating power shaft 10 drives the primary and secondary booster pistons 12, 14. Utilizing the Pascal principle of hydraulic transmission, the boosting capacity of these pistons is determined by the ratio of their end areas. These pistons contain channels for CO2 flow, and one-way relief valves are installed at the ends of each piston, allowing the CO2 to pass through the primary and secondary booster units 11, 13, and accumulate in the mixing chamber.

[0070] Principle of mixing supercritical CO2 and proppant. To ensure thorough mixing of the supercritical CO2 and proppant in mixing chamber 15, the proppant particles must have the same density as the supercritical CO2. For example, for resin-coated ceramsite proppant, the density of the proppant and supercritical CO2 can be adjusted by adjusting parameters such as the porosity of the ceramsite and the coating thickness.

[0071] Because supercritical CO2 has a significant impact on increasing oil and gas field production, CO2 formation injection technology is gradually being applied to oil and gas development. Furthermore, the storage of CO2 in underground spaces such as the seabed, coal seam goafs, and saline aquifers can help achieve my country's "dual carbon" goals.

[0072] In response to the technical difficulties of formation carbon injection technology, the present invention proposes a downhole CO2 transcritical pressurization method, which uses the central channel 6 of the double-wall drill pipe to transport drilling fluid to provide power for the downhole pressurization system. The low-pressure gaseous CO2 is transported to the downhole pressurization system through the annular gap 5 of the double-wall drill pipe. After passing through the first-level pressurization unit 11, the low-pressure gaseous CO2 is pressurized to a supercritical state, and the second-level pressurization unit 13 further pressurizes the CO2 to the target pressure value.

[0073] The downhole CO2 transcritical pressurization method proposed in the present invention can accurately control the phase change process of CO2, prevent supercritical CO2 from corroding surface equipment and well pipelines, reduce the high pressure and corrosion resistance requirements of surface equipment, and is applicable to a wider range of terrains and fields, thereby helping to achieve efficient carbon injection and providing technical support for my country's oil and gas resource development and carbon sequestration projects.

[0074] The circulating drilling fluid is used as the power medium to drive the downhole pressurization system, and the low-pressure gaseous CO2 is pressurized to a high-pressure supercritical state in the formation.

[0075] Double-wall drill pipe is used to transport drilling fluid and gaseous CO2 in the well. The central channel of the double-wall drill pipe transports drilling fluid, which serves as the motive force for the downhole pressurization system. The drilling fluid is returned to the orifice through the annular space between the double-wall drill pipe and the well casing. The annular space of the double-wall drill pipe transports low-pressure gaseous CO2.

[0076] The present invention proposes a method for underground carbon dioxide transcritical pressurization, in which low-pressure gaseous CO2 is injected into the formation through a pipeline in the well, and the gaseous CO2 is first pressurized to a supercritical state in the formation using a downhole pressurizing device, and then the supercritical CO2 is pressurized to a target pressure value. By means of step-by-step pressurization, transcritical pressurization of CO2 is achieved to meet engineering requirements such as formation fracturing, oil recovery and production increase, crude oil extraction, and formation carbon storage. The purpose of the present invention is to pressurize CO2 gas to a supercritical state underground. Compared with surface pressurization technology, this method can effectively avoid the corrosion of the well pipeline by supercritical CO2 and reduce the proportion of surface carbon injection equipment. In particular, in the field of seabed carbon injection and storage, there is no need to equip expensive fracturing vessels, which can significantly save economic costs.

[0077] The first-stage booster unit 11 operates on the Pascal principle of hydraulic transmission. The boost ratio is determined by the area ratio of the pistons at both ends. The first-stage booster unit 11 boosts the low-pressure gaseous CO2 to a supercritical state. The second-stage booster unit 13 operates on the same principle as the first-stage booster unit 11, boosting the supercritical CO2 to a higher pressure to meet carbon injection requirements.

[0078] When supercritical CO2 meeting the carbon injection pressure passes through the mixing chamber, the supercritical CO2 is mixed with the proppant.

[0079] When the mixed fluid of supercritical CO2 and proppant passes through the pump-out chamber 16, the pressure of the mixed fluid exceeds the opening pressure of the relief valve, the relief valve 17 opens, and the mixed fluid is pumped out of the booster system. Under the sealing effect of the packer, the formation is fractured and enters the formation. The proppant is used to support the cracks to prevent the cracks from closing after the fracturing fluid is discharged back.

Claims

1. A downhole carbon dioxide transcritical pressurization equipment, characterized by: It includes a double-wall drill pipe (4), a packer and a downhole pressurization system; The double-wall drill pipe (4), the packer and the downhole pressurization system are all arranged downhole, and the number of the packers is more than three; A casing (7) is provided outside the double-wall drill pipe (4), and the portion of the casing (7) outside the well is connected to the inlet of a cyclone desander (3), the outlet of the cyclone desander (3) is connected to the inlet of a mud pump (2), and the outlet of the mud pump (2) is connected to the central channel (6) of the double-wall drill pipe (4); the annular gap of the double-wall drill pipe (4) is connected to a carbon dioxide tanker (1); The downhole boosting system comprises a screw motor (8), a screw joint (9), a power shaft (10), a first-stage boosting unit (11), a first-stage boosting piston (12), a second-stage boosting unit (13), a second-stage boosting piston (14), a mixing chamber (15) and a pump-out chamber (16); The screw motor (8) is connected to the power shaft (10) via a screw joint (9), and the screw joint (9) and the power shaft (10) are connected in a sleeve connection manner. A pin shaft (21) is provided on the screw joint (9), and a track groove corresponding to the pin shaft (21) is provided on the power shaft (10); The power shaft (10) is connected to the first-stage booster piston (12) and the second-stage booster piston (14) in sequence. The first-stage boosting unit (11) and the second-stage boosting unit (13) are both piston cylinders, each of which is provided with a first-stage boosting piston (12) and a second-stage boosting piston (14); The secondary boosting piston (14) passes through the packer and is connected to the mixing chamber (15), and the mixing chamber (15) passes through the packer and is connected to the pump-out chamber (16); A proppant is provided in the mixing chamber (15); The ends of the first-stage boosting unit (11) and the second-stage boosting unit (13) are both provided with overflow valves (17).

2. The downhole carbon dioxide transcritical boosting equipment according to claim 1, characterized in that: A central channel is provided in the screw motor (8), and one end of the central channel is connected to the annular gap of the double-wall drill rod (4).

3. The downhole carbon dioxide transcritical boosting equipment according to claim 1, characterized in that: The screw joint (9) performs rotational motion, and the pin shaft (21) cooperates with the track groove, so that the power shaft (10) performs reciprocating motion in a straight line.

4. A method for downhole carbon dioxide transcritical pressurization, using the downhole carbon dioxide transcritical pressurization equipment according to any one of claims 1 to 3, characterized in that The following steps are included: And the following steps are carried out in sequence: Step 1 After the vertical well and the horizontal well are drilled, a packer and a downhole pressurizing system are lowered; the mixing chamber (15) of the downhole pressurizing system is pre-filled with a proppant; Step 2 The double-wall drill pipe (4) is installed and connected to the downhole boosting system; the carbon dioxide tanker (1) is connected to the annular gap of the double-wall drill pipe (4), and the carbon dioxide enters the first-stage boosting unit (11) and the second-stage boosting unit (13) through the central channel of the screw motor (8); Step 3 The mud pump (2) is connected to the central channel (6) of the double-wall drill pipe (4), and the mud pump (2) transports the drilling fluid into the central channel (6); the screw motor (8) rotates under the pressure of the drilling fluid, and the screw motor (8) drives the screw joint (9), and the power shaft (10) performs linear reciprocating motion under the cooperation of the pin shaft (21) and the track groove, driving the first-stage booster piston (12) and the second-stage booster piston (14) to work; Step 4 After the driving in step 3, the low-pressure gaseous carbon dioxide delivered by the carbon dioxide tanker (1) is pressurized by the first-stage pressurizing unit (11), and the carbon dioxide is pressurized to a supercritical state. The supercritical carbon dioxide is further pressurized in the second-stage pressurizing unit (13) to form supercritical carbon dioxide with a higher pressure; Step 5 The supercritical carbon dioxide obtained in step 4 is mixed with the proppant in the mixing chamber (15) to obtain a mixture; the mixture enters the pump-out chamber (16), the overflow valve (17) is opened under the action of pressure, and the mixture of the supercritical carbon dioxide and the proppant passes through the overflow valve (17) into the closed space isolated by the packer (18), and the mixture is injected into the bottom carbon storage space under the action of pressure; Step 6 The mixture injected into the bottom layer has a corrosive effect on the surrounding rock formations, causing rock blocks to peel off; the mud pump (2) and the carbon dioxide tanker (1) stop working, and the downhole booster system performs a pressure relief operation. The peeled rock blocks and the mixture jointly support the cracks, forming a stable carbon storage space.

5. The downhole carbon dioxide transcritical pressurization method according to claim 4, characterized in that: Before running into the downhole pressurization system in step 1, the density of the pre-filled proppant should be determined according to the density of supercritical carbon dioxide at the target pressure value. The density of the proppant can be adjusted by controlling the porosity of the proppant particles or the thickness of the resin coating.

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